Syllogism
by Osmodion
Summary: Syllogism:a form of deductive reasoning using two or more premises to arrive at a logically valid conclusion. When a Tom Riddle-lookalike starts appearing around Hogwarts, Harry, Hermione, and Ron (well, mostly Hermione) come up with the brilliant plan to ascertain his identity-by using a truth-telling secrecy sensor. -ONESHOT- *Cleaning out my stories*


Kinda confusing short explanation about the logic behind this at the bottom. :)

* * *

Harry tore through the halls of Hogwarts, dodging around sleepy students. He earned a couple of curses, mainly from the Slytherins, and a couple of giggles and cheers, mainly from the Gryffindors. The Ravenclaws glared and the Hufflepuffs just smiled and secretly planned world domination.

Well, that last part wasn't completely accurate, but who could blame him? Especially since so many of the more ridiculous rumors all centered around him.

He ran through a chilly Nearly Headless Nick and narrowly missed hitting a very solid banister. Turning the corner, he rushed into the library and glared at the stupid librarian when she aggressively shushed him.

Stupid lady.

Catching sight of a tousle of brown hair and a flash of red peeking out above a low bookcase, he found a half secluded table and stopped to catch his breath.

He rattled the chain of the necklace.

"Ssshhhhh!" hissed the librarian.

Ron and Hermione raced over and huddled over him. "Harry-" Ron started. "-What did you find?" Hermione finished urgently.

"He's not." Harry said. "Oh Merlin, he's not."

Ron collapsed into a chair.

"Are you sure?" Hermione pressed. "Did you make him say the words? Did it vibrate?"

"W-well," Harry stammered. "Not...exactly."

Hermione stomped her foot. "Harry! Then what do you mean he's _not_?"

"Er...well, I asked him if he was, and he said..." Harry paused, working over the memory. He rubbed the smooth surface of the pendant, frowning. Had the secrecy sensor actually worked?

He felt his stomach drop. He had been fooled...hadn't he?

"What did he say?" Ron whispered, pale. Hermione stared at him intently.

"Uh..."

"Oh, for crying out loud!" Hermione hissed. "Let's go to McGonagall's office and use her pensive."

"Pensive?" Harry shared confused looks with Ron. "What's a pensive?"

Now it was Hermione's turn to look uncomfortable. "Well...I haven't been exactly truthful with you guys..."

Ron's face turned an angry red. "I hope it hasn't got anything to do with this...this...mess we're in! If you've been hiding something about him...or Ginny...then...I won't forgive you!"

Hermione glared, but her eyes started to glisten.

Harry turned to Ron, exasperated. "Just listen to what she says! Hermione's never been anything but a good friend to us."

Ron shut up and blushed. Harry shook his head and waited for Hermione to speak up again.

"Um...McGonagall gave me some...magical artifacts to help me with my studies, since I was a muggleborn. I've got a time-turner, and McGonagall lets me use the pensieve in her office to store memories of my lectures." She looked at each of them defiantly, expecting another outburst.

"Blimey, Hermione!" Ron exclaimed. "You've got a time-turner?"

"Yeah," Hermione said, surprised. "It's really useful for extra research." She started to smile, then hesitated. "But that's not what's important. We can use the pensieve to watch Harry's memories."

Harry furrowed his brow. "Why not just go back in time? My memories are a little fuzzy, and I might have not noticed something."

"That would be so cool!" Ron grinned excitedly. "I bet my brothers have never gone back in time."

"No." Hermione said firmly. "Mrs. McGonagall gave me a list of rules to follow that you can _never_ break when you're using a time turner. If you break them, then you'll destroy the flow of time. Using the pensieve is much safer, and it remembers stuff that you've forgotten."

"But what about if I didn't notice something important?" Harry asked.

"Well, that's okay. We only need to know if he was, you know." She looked uncomfortable.

"Voldemort." Harry finished, darkly.

Ron looked worried again. "Are you sure he looked like that when he was younger? I mean-" he started quickly, "he's a Slytherin and all, but he doesn't, I don't know, _look_ like...Vol-vol-" He glanced beseechingly at Harry.

"Voldemort. I know. Last year, he tricked me, too, in the chamber. But it was him. He killed Ginny, and he almost killed me." Harry stared at both of them. "I think it's him. He's after me. He thought I was dead, after I fainted when the Basilisk bite me, but he didn't know that Fawkes' tears can heal Basilisk bites, I guess. At least, I _think_ it's him. He was...weird."

Ron looked at him. "Well, let's go find out."

"Come on, Harry. Let's go to McGonagall's room."

* * *

"Syllogism."

"Wha-?" Ron was flabbergasted. "Who uses a password like _that_? What is that, anyways?"

Harry watched patiently as the cabinet door opened to reveal some sort of stone pot with a shallow metal basin. "So..." he started. "How does it work?"

"You're supposed to take out a memory using your wand and then put it in the basin." Hermione instructed.

"I...what?"

"You put your wand so that its touching your head, like so..." Seeing Harry's improper positioning, she huffed and gave up. "You know what, just let me do it for you."

Five minutes later, Hermione dropped the silvery glob of memories into the pensieve.

"Gross." Ron whispered. "Looks like snot."

"Shut up!" Hermione hissed.

"Um, so..." Harry eyed the glowing pool of memories. He still hadn't recovered completely from the feeling of having someone take out a memory, ugh. Imagine having _that_ drawn out of an ear. "What do we do now?"

"We put our faces in." Hermione said, as if that was the most natural thing to do.

"What?" Ron said faintly.

"We put our faces in that? How is that supposed to do anything, exactly?" Harry questioned, feeling slightly sick. He had just had _that thing_ extracted and now they were supposed to just plonk themselves face first...

"Won't it get, um, in our noses? Or in our mouths?"

"Honestly. Are you seriously going to stop someone who could be a _dark lord_ just because you're afraid of a little water?" Hermione asked crossly.

Ron paled. "But it's _not_ water, Hermione."

"Oh, shut up, Ron. It's just easier to think of it that way."

Harry and Ron glanced at each other. "Here goes nothing..."

They slammed their faces into the metal.

* * *

Harry watched as he ran up to Tom Riddle. He had been no less shocked the third time he had met Riddle than the second. He kept thinking that he had been hallucinating, but no.

Riddle was sitting on one of the desks in the potions classroom, looking outside to the Forbidden Forest, and what lay beyond. His back was irritatingly straight, his legs regally crossed, and his hands resting, clasped, upon his knees. Snape was nowhere to be found.

Harry watched himself stop a meter away from the monster. His wand was gripped tightly in a white-knuckled hand.

"Who are you?" Harry snarled.

Without turning around, Riddle simply said, "I am not what you think I am."

For his lack of motion, Riddle could have been a statue.

"Are you-are you Voldemort?" he asked.

"Quick!" Hermione yelled. "If he says yes...we need to see if the sensor vibrated!"

Hermione's outburst startled him out of his reverie. He was half surprised that the memory Riddle and the memory him hadn't reacted to the yell.

Ron clambered over to memory Harry. "I found it!"

Riddle shot him a calculating look. "And if I say yes?"

Hermione grumbled.

"You won't get out of here alive."

"I am Voldemort." Riddle cocked a perfect brow.

Harry clutched his wand tighter, and his heart clambered. He hadn't felt the secrecy sensor vibrate. Had it been a fluke? Maybe the vibrations had been too soft, maybe it was muffled by his clothes...he hadn't really been paying attention. He forced his mouth to move, shape words.

"Are you telling the truth?"

Riddle smiled, disarmingly. Gently, he said,"I am lying."

Harry paused, waiting for the vibrations, but none came. Now...that didn't make any sense. He glanced speculatively at the possible murdering megalomaniac. "Are you lying about something other than the issue? Are you lying about something that you're thinking in your head?"

"These are specific questions, Potter. But, I am talking about my identity as you see it, and not lying about what I'm thinking in my head. In fact, I am thinking about nothing other than my identity. What I have said twenty-three point four seconds ago reflects the truth of my identity. And no, I am not distorting your senses or influencing you in any other way." He paused and grinned. "Do you have any more questions? That covers it all, doesn't it?"

Now that Harry noticed, the teenager looked a bit childish, with his legs swinging slightly back and forth. He twirled a wand in his hand, but was making no move to harm Harry.

Harry looked at the kind face, and swallowed.

"Uh...well, are you sure?" he tried.

"Yes, Harry, I am _sure_ that I am lying." The teenager rolled his eyes. "You should head back. Classes will resume soon, and nothing's worth a detention from Snape, believe me." He snorted.

Harry started to put his wand away. "Erm, sorry about that. Paranoia, you know. Gets to me sometimes."

"No worries," the teenager assured him. "Happen to me, too, if I were you. Can't trust dark lords. See ya." He raised his arm in mock salute and smirked, eyeing Harry conspiratorially, like they were best friends sharing some big secret.

Harry stood uncomfortably. "Well...see ya." He smiled uncertainly and rushed out of the room.

The mindscape faded out around them.

* * *

"The sensor didn't vibrate. Not once." Hermione whispered.

"I guess, he isn't really you-know-who, then." Ron added hopefully.

Harry started to pace. "No, he's not." There was a nagging at the back of his mind. "But he's_ supposed_ to be, right? He looks exactly the same. I'm sure of it now." He hands shook in frustration. "I don't _get it_." It looks like him, but it isn't him. "And how did he make the sensor not work?"

He collapsed into a chair. "I'm so confused!"

Suddenly, a lock slide into place. They all froze in fear.

"Well, well, well," came a sibilant, satisfied voice. "What do we have here? Three little lost sheep. Or little lions, but they're all the same to me."

"Wha-what?" Ron's eyes grew as wide as saucers as he put the pieces together. Hermione and Harry blinked up in shock but within seconds, had their wands aimed, at the ready.

"How did you find us?" Hermione cried while Ron shouted, "McGonagall and the other teachers will find you!"

"Tsk. tsk. So rude. Uncultured filthy cretins." His dark gaze bore over them and they seemed to shrink within themselves. "Did you really think I would expose myself to the student body or the teachers? Idiotic riffraff."

"Voldemort." Harry surprised himself with the lack of inflection in his voice. He was still trying to wrap his mind around the two Riddle personas.

Riddle dipped his head in acknowledgement. "Harry, our little cockroach. Can't just settle down and die, can you?"

"How did you evade the secrecy sensor?"

"We tested it. It worked." Ron defended.

Riddle looked amused. "I would think that you would have, but perhaps your stupidity knows no bounds. And as for evading it, the reason was simple."

He smirked. "A secrecy sensor cannot sense that which is not a lie or a truth."

"But you are Voldemort! Even if you are the younger version of him, you are Voldemort!" Harry argued.

Hermione looked pensive. "Does it not work because there are two Voldemorts in the world?"

"No!" Riddle said sharply. "Fools. I am Voldemort, and essentially, there is no difference between him and I."

Ron tried to shoot an _expelliarmus_, but he found that his wand had disappeared. Hermione gasped at the lack of weight in her hands, while Harry glared defiantly.

Riddle looked upon them with thinly-veiled disgust. "The statement is outside of the bounds of truth and lie, and outside the bounds of the sensor. It is logically unsound. There is no method to say 'I am lying.' and be correct."

At their uncomprehending and terrified looks, he hissed, "Do they teach nothing of value anymore? Simple minded fools, the lot of you!"

He snarled and petrified them with an almost instantaneous flick of the wrist. "Pathetic. And _this_ is the Golden Boy and his third-year servants. I wish I could have given you a more painful death. Oh, and Harry?"

His saccharine smile was choking.

"I hope you have the sense to stay dead this time. _Avada Kedavra_."

* * *

He was lying underneath a bench at the King's Cross Station.

Groggily, he thought he heard faint voices of mourning far away.

It was his duty to follow them and save him, was it not?

* * *

Since some people were confused by the fic, I guess I'll take some space to explain it a bit.

If you've ever heard of knights and knaves logic puzzles or the Cretin paradox, go back and reread the fic. You've simply missed it. For those who don't have a lot of background in formal logic reasoning, well:

"I am lying" is a paradox because it just doesn't work.

We can take it in two senses:

One, that when I say "I am lying," the statement is true. If "I am lying" is a true statement, that means that when I say that I am lying, I mean that I am lying. In other words, I wasn't lying about the fact that "I am lying," I was telling the truth. Rather obviously, we notice that we run into a problem. If I am telling the truth, then "I am lying" is true, but, in the world of formal logic, I can't be lying and telling the truth at the same time.

Two, that when I say "I am lying," the statement is false. In this case, I actually am lying about whether or not "I am lying." Since "I am lying" is false, I am actually not lying. We can assume that not lying essentially means telling the truth (although, really, it doesn't.) Now we notice that, oh no! There is paradox because I can't be simultaneously lying and telling the truth.

A (kinda?) easier to understand diagram:

Pretend Tom Riddle has two characteristics, 1.) what he is and 2.) what his words say about him.

1.) What he is=either truthful or lying

2.) What his words say about him=either truthful or lying

In the world of formal logic, 1=2 is necessary.

If 1=truthful then 2=lying.

If 1=lying then 2=truthful.

Therefore, the secrecy sensor couldn't pick the "lie" up, because it wasn't actually a lie. I think it would be cool if the secrecy sensors had a built-in explosion mechanism that was triggered by a paradox or half-truth. Plus, St. Mungo's could sponsor the development and get more revenue from even more wizards in the hospitals!

Toodles~


End file.
